Industrial-rated circuit breakers are available having operating components that are designed for automatic assembly to provide cost improvement as well as improved operating efficiency. The precision alignment performed by the automated assembly equipment allows the operating components within the circuit breaker operation mechanism to be installed within very close operating tolerances. The operating mechanism assembly includes a pair of powerful operating springs that are overcentered for rapidly driving the movable contact arm and the attached movable contact away from the stationary fixed contact to interrupt the circuit current. The operating mechanism includes a cradle operator which engages a latch assembly to prevent the movable contact arm from being driven to its open position under the urgence of the charged operating springs. The compact latch assembly includes a primary and secondary latch operating within a common support structure.
An overcurrent condition is determined within the electronic trip unit such as described within U.S. Pat. No. 4,658,323 and a trip signal is outputted to the trip actuator to articulate the circuit breaker operating mechanism to interrupt the circuit current. The circuit current is sampled continuously through three current transformers one for each of the three current phases. The trip actuator is described within U.S. Pat. No. 4,679,019 and the current transformers are described within U.S. Pat. 4,884,048. To protect the current transformers from the debris resulting from the arc gases generated under intense overcurrent interruption, the three current transformers within the three-pole circuit breakers are encapsulated together in a plastic composition and are inserted within the circuit breaker case as a single unit. This requires a different-sized current transformer unit for each circuit breaker frame size since the circuit breaker enclosures increase in size according to the ampere rating requirements with each frame.
Since the individual current transformers are capable of use within the various frame sizes without modification, it has been determined that a substantial cost savings can be realized if the current transformer arrangement described within the aforementioned U.S. patent could be simplified.
Accordingly, one purpose of this invention is to describe an arrangement wherein the current transformers used within circuit breakers employing electronic trip units can be individually mounted within the circuit breaker enclosures of various ampere ratings without encapsulating the current transformers as a single unit.